JPS598156B2 - AC variable speed electric motor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a variable speed drive device for a synchronous motor, which suppresses an increase in motor terminal voltage due to a change in armature current in response to sudden load fluctuations. Regarding.

AC variable speed motors using synchronous machines can be roughly divided into two types, depending on the waveform of the input current: square wave drive systems and sine wave drive systems.

Most conventional AC variable speed motor devices use the former square wave drive method, which consists of a synchronous motor that can vary the field current depending on the speed and load condition, and the actual speed signal and speed of this motor. The synchronous motor is combined with a thyristor conversion device that changes the current command signal based on the deviation from the command signal and determines the firing phase of the thyristor element by comparing it with the actual current value to control the synchronous motor at variable speed. .

However, in such variable speed electric motor devices, there are not many measures taken against overload capacity and sudden load fluctuations due to the set commutation lead angle and commutation overlap angle, and for example, as a system for steel rolling. When using,
Particularly when there is a sudden load change, that is, when moving from a heavy load to a light load, the motor terminal voltage becomes overvoltage due to the relationship between the sudden change in armature current and the field response speed. There are many examples of designs with a margin. This is because in the conventional non-commutator motor, the relationship between the position of the motor field magnetic pole and the current phase is constant. On the other hand, even in the case of a sine wave drive system, there are currently not many measures taken against overload or rapid load fluctuations.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to prevent a rise in motor terminal voltage due to a sudden change in load, reduce the design margin for overvoltage of a converter, and
It is an object of the present invention to provide an AC variable speed electric motor device that can reduce costs.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a typical system configuration of an AC variable speed electric motor device. That is, in Figure 1, 1 is 3
It is a sine wave output cycloconverter (frequency converter) with phase input and three phase output.The input terminal is connected to an AC power supply (not shown) via the transformer 2, and the output terminal is connected to the input of the same machine motor 3 with a neutral point. Connect to the terminal. The cycloconverter 1 has a configuration for each output phase, such as two six-arm bridges connected in parallel, a cross connection, or four bridges connected in H. Also, 4
A field current converter is connected to an AC power source (not shown) via a transformer 5, and this converter 4 connects the field current to the field winding of the synchronous motor 3. Reference numerals 6 and 7 indicate a sershin and a tacho generator directly connected to the synchronous motor 3. The sershin 6 detects the position of the field magnetic pole, and the tacho generator 7 detects the rotation speed.

On the other hand, the speed control system is roughly divided into two systems: the armature current control system and the field current control system. First, the armature current control system will be described.

The speed detection signal detected by the tacho generator 7 is applied to a comparator 8 together with the speed reference signal for comparison, and the difference is applied as a speed deviation to a speed control circuit 9 consisting of a proportional-integral circuit, and the output is sent to an electric machine whose details will be described later. Child current reference circuit 10
Add to. Further, the position detection signal of the field magnetic pole detected by the Celsin 6 is applied to the synchronous rectifier circuit 11 to obtain a sine wave signal with a constant peak value corresponding to the rotor position, and this is applied to the armature current reference circuit 10. The above armature current reference circuit 10
As shown in FIG. 2, the phase of the synchronous rectification signal is set at a certain angle θ. a power factor control circuit 12 that produces a zero-shifted signal;
A multiplication circuit 13 that multiplies the constant peak value signal phase-shifted by the power factor control circuit 12 by the speed control signal, a differentiation circuit 14 that differentiates the speed control signal, and a waveform that shapes the differential output of the differentiation circuit 14. a shaping circuit 15; a multiplier circuit 17 that multiplies the differential output waveform-shaped by the waveform shaping circuit 15 by a signal obtained by advancing the synchronous rectified signal by 90 forces by the shift circuit 16; It is composed of a multiplier circuit 19 that multiplies a signal obtained by inverting the differential output by a negation circuit 18 and the output signal of the multiplier circuit 13, and an analog adder circuit 20 that adds the output signals of these multiplier circuits 17 and 19 in an analog manner. .

The comparison circuit 22 compares the current reference signal obtained from the armature current reference circuit 10 having such a configuration with the current value extracted from the input current of the cycloconverter 1 through the rectifier circuit 21, and the difference output is sent to the α control circuit 23. Add to.

This α control circuit 23 controls the firing phase angle of the thyristor element of the cycloconverter 1 based on the deviation output from the comparison circuit 22. Next, to describe the field current control system, reference numeral 24 denotes a field current control circuit to which the speed deviation signal from the comparator circuit 8 and the speed detection signal from the tacho generator 7 are applied. The field current standard is set based on the deviation and speed.

The comparison circuit 26 compares the field current reference value set by the field current control circuit 24 and the current value taken out from the input current of the field current converter 4 through the rectifier circuit 25.
The deviation output is applied to the α control circuit 27. This α control circuit 27 controls the firing phase angle of the field current converter 4 based on the deviation output from the comparison circuit 26. Next, the operation of the AC variable speed electric motor device configured as described above will be described.

Now, assuming that the synchronous motor 3 is operating under a steady load condition, the speed deviation signal at this time is the tachogenerator 7
The speed detection signal detected by is small because it has a value close to the speed reference, and the speed control circuit 9 proportionally integrates the small speed deviation signal and supplies it to the armature current reference circuit 10. In addition, a position detection signal of the field magnetic pole detected by the Celsin 6 is added to the synchronous rectifier circuit 11.
This synchronous rectification circuit 11 synchronously rectifies the position detection signal and converts the sine wave signal with a constant peak value into an armature current reference circuit 10.
is giving to The armature current reference circuit 10 performs the following signal processing based on the signals supplied from the speed control circuit 9 and the synchronous rectification circuit 11, and outputs an armature reference current. That is, under steady load, the speed of the synchronous motor 3 is substantially constant, so the speed control signal output from the speed control circuit 9 at that time has a constant value and is applied to the differentiating circuit 14. Therefore, since the output of the differentiating circuit 14 at this time is 0'', the output of the waveform shaping circuit 15 also becomes 0'' and is applied to the multiplier circuit 17 and the multiplier circuit 19.
is inverted by an inverting circuit 18 and has an output added thereto.

On the other hand, a sine wave signal with a constant peak value obtained from the synchronous rectifier circuit 11 generates a signal whose phase is shifted by a certain angle by a power factor control circuit 12, and this signal is multiplied by the speed control signal by a multiplier circuit 13, Furthermore, the output is multiplied by the output "1" of the negation circuit 18 by the multiplier circuit 19 and applied to the analog adder circuit 20. In this case, the synchronous rectified signal is applied to the 90-way shift circuit 16, and a signal shifted by 900 is obtained. However, since this signal is multiplied by the ``O'' output of the waveform shaping circuit 15 by the multiplication circuit 17, the output of the multiplication circuit 17 becomes 0. Therefore, under steady load conditions, the synchronous rectification signal is controlled by the power factor control circuit 12 at a certain angle θ.

. A signal obtained by multiplying the shifted signal and the speed control signal becomes the current reference signal. The current reference signal obtained in the armature current reference circuit 10 in this way is compared with the input current of the cycloconverter 1 obtained through the rectifier circuit 21 by the comparator circuit 22, and the deviation signal is added to the α control circuit 23 and the cycloconverter Controls the firing phase angle of the thyristor of converter 1.

In addition, in the field control system at this time, the field current control circuit 24 sets a field current reference based on the speed detection signal and speed deviation signal detected by the tacho generator 7, and the field current reference is set by the comparison circuit 26 through the rectifier circuit 25. The deviation signal is applied to the α control circuit 27 to control the firing phase angle of the thyristor of the converter 4.

In such a situation, if there is a sudden load change,
The armature current reference circuit 10 performs the following signal processing and outputs an armature reference current.

Now, if we consider a rapid load decrease as a load change, the value of the speed deviation signal will increase in this case, so the speed control circuit 9
The speed control signal output from increases in the positive direction.
When such a speed control signal is applied to the differentiating circuit 14, the differentiating circuit 14 sends out a differentiated output signal for a period approximately equal to the response time of the field current. In this case, while the differential output signal is above a certain positive level, the output is 61''.The output signal of the differentiating circuit 14 is waveform-shaped by the waveform shaping circuit 15, and an output of 1 is added to the multiplier circuit 17, and the inverter・O゛ output inverted by 18 is multiplier circuit 1
Join 9. On the other hand, the signal synchronously rectified by the synchronous rectifier circuit 11 at this time is advanced by 90 steps by the 90 shift circuits 16, and its output signal is applied to the multiplier circuit 17 and multiplied by the ``1'' output of the waveform shaping circuit 15. , added to the analog adder circuit 20. In this case, the output of the power factor control circuit 12 and the speed deviation signal are multiplied by the multiplication circuit 13;
The multiplication output is further multiplied by the output ``0'' of the NOT circuit 18 in the multiplier circuit 19, so that the output applied to the analog adder circuit 20 is 60 degrees. Therefore, when there is such a sudden load reduction, a signal obtained by advancing the synchronous rectification signal by 90 is sent out from the armature current circuit 10 as the armature reference current. The armature reference current obtained in this way is compared with the input current of the cycloconverter 1 obtained through the rectifier circuit 21 by the comparator circuit 22 in the same way as described above, and the deviation signal is applied to the α control circuit 23, and the thyristor of the cycloconverter 1 is ignition phase angle.

Further, regarding the field control system at this time, the field control is performed by the same signal path as described above, so the explanation thereof will be omitted here.

Next, the reason why the armature current reference circuit 10 as described above can suppress the rise in terminal voltage by changing the armature current during sudden load changes (rapid load reduction) will be explained in comparison with the conventional case. .

The AC variable speed motor device according to the present invention is the same as a conventional synchronous motor drive device using a sine wave current control method except when the load suddenly decreases.

However, if this conventional current control method is applied even when the load suddenly decreases, problems as described in the vector diagram below will occur. That is, for the sake of simplicity, it is assumed that the rotating machine is a cylindrical rotor with no winding resistance, and the vector relationship under steady load is as shown in FIG. In Figure 3,
EO is the no-load induced voltage, I is the armature current, θo is the power factor control angle, E is the terminal voltage, and X is the synchronous reactance. This vector diagram is the same for both the control system according to the present invention and the conventional control system. However, in the conventional current control method, when a sudden load decrease occurs, the vector relationship at that time is
The result will be as shown in the figure. As is clear from this vector diagram, the armature current 1 has become very small, but since the field magnetic flux has not been reduced enough, the terminal voltage E has increased significantly. On the other hand, according to the current control method according to the present invention, the power factor control angle θ is determined as shown in the vector relationship shown in FIG.

Since the armature current 1 is advanced by 90 and the effective value of the armature current 1 is kept constant, only the demagnetizing effect acts on the motor voltage and no output torque occurs. This state can be maintained until the field current responds, and after the response, the conventional current control method can be used. Therefore, if the armature current is controlled using the current control method as described above when the load suddenly decreases, the terminal voltage E of the motor will not increase and the voltage applied to the converter will be reduced, as is clear from the vector relationship shown in Figure 5. It becomes a safe system. Moreover, since there is no need to change the field current too rapidly, the field excitation capacity can also be reduced. Note that in the above embodiment, the power factor control angle θ changes when the load suddenly decreases.

The power factor control angle θ was advanced for 90 cases. is the differential circuit 1
4 (shown in FIG. 2) or may be changed functionally in correspondence with the field current without any problem. Furthermore, the peak value during this period may also be changed functionally. In addition, the present invention can be implemented with various modifications without changing the gist thereof. As described above, according to the present invention, it is possible to prevent the motor terminal voltage from increasing due to sudden changes in load, reduce the design margin for overvoltage of the converter, and reduce the field power capacity of the motor, thereby reducing costs. It is possible to provide an AC variable speed electric motor device that can achieve the following.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the AC variable speed motor device according to the present invention, FIG. 2 is a block diagram showing the configuration of the armature current reference circuit in FIG. 1, and FIG. 3 is a block diagram showing the configuration of the armature current reference circuit in FIG. Figure 4 is a simplified vector diagram of the motor when the load suddenly decreases in the conventional current control method.
FIG. 5 is a motor vector diagram when the load suddenly decreases in the current control method according to the present invention. 1...Cycloconverter, 3...Synchronous motor, 4...Converter, 6...Selsyn, 7...Tacho generator, 9・・・・・・
・Speed control circuit, 10... Armature current reference circuit, 11... Synchronous rectification circuit, 12... Power factor control circuit, 13, 17, 19...・Multiplication circuit,
14... Differentiation circuit, 15... Waveform shaping circuit, 16... 90 times shift circuit, 18...
...Negation circuit, 20...Analog addition circuit,
21, 25... Rectifier circuit, 24... Field current control circuit, 23, 27... α control circuit.

Claims (1)

[Claims] 1. A synchronous motor, a thyristor conversion device that supplies frequency-converted alternating current electricity to the synchronous motor, a speed control circuit that proportionally integrates a deviation between an actual speed signal of the synchronous motor and a speed reference signal, and a field of the synchronous motor. A synchronous rectifier circuit that synchronously rectifies the magnetic pole position detection signal to obtain a sine wave signal with a constant peak value, and outputs from the synchronous rectifier circuit during a steady load state in which the deviation between the actual speed signal of the synchronous motor and the speed reference signal is small. A signal obtained by multiplying a signal obtained by shifting a synchronous rectified signal by a constant angle by a power factor control circuit and a proportionally integrated speed control signal output from the speed control circuit is used as a current reference signal, and is used as the actual speed signal. An armature current reference circuit that uses, as a current reference signal, a signal obtained by advancing a synchronous rectification signal outputted from the synchronous rectification circuit by a predetermined angle by a phase shift circuit during load fluctuations with a large deviation from the speed reference signal, and this armature current reference. a first control device comprising a circuit that controls a firing phase angle of a thyristor element of the thyristor conversion device by comparing a current reference signal output from the circuit with an actual current value flowing through the armature of the synchronous motor; A field current control circuit that sets a field current reference based on a speed deviation signal between an actual speed signal and a speed reference signal of the synchronous motor and the actual speed signal, and a field current reference signal output from the field current control circuit. and a second control device comprising a circuit for controlling field current based on a deviation signal from the actual field current of the synchronous motor.